1. Field of the Invention
The present invention relates to an apparatus and a method for determining the type of an electromagnetic wave generating source for determining the type of a generating source of an electromagnetic wave emitted from electronic equipment.
2. Description of the Related Art
In recent years, to minimize EMI (Electromagnetic Interference) due to radiation emitted from electronic equipment, many countries establish controls over permissible values of electromagnetic waves emitted from electronic equipment. For example, in overseas countries, agencies such as FCC (Federal Communications Commission), CISPR (Comité international spécial des perturbations radioélectriques (International Special Committee on Radio Interference)), and VDE (Verband Deutscher Elektrotechniker (Association of German Electrical Engineers)) set standards. In Japan, VCCI (Voluntary Control Council for Information Technology Equipment) sets voluntary control standards, and electronic equipment manufacturers try to reduce EMI radiation emitted from electronic equipment.
For such standards, methods for measuring EMI radiation include a method for measuring electric field strength in a position a predetermined distance (for example, 3 or 10 m) apart from electronic equipment that is a generating source of EMI radiation. This method is generally referred to as “far field measurement”. A standard value of this method is referred to as a “far field measurement standard value”. The method uses special measurement environment or measurement devices, and requires considerable expertise in measurement. Also, because of the far field measurement, it is difficult to identify the generating source of an electromagnetic wave in the electronic equipment. Thus, EMI radiation measures require enormous amount of time and costs. Thus, recently, to reduce time and costs, a measurement device is used near, for example, a printed circuit board of electronic equipment that emits an electromagnetic wave to measure electromagnetic field strength. Further, to reduce time and costs, a demand is increasing for a method for estimating a far field measurement standard value using a measurement result of a measurement device.
Such a measurement device includes, for example, a device that scans a near field of an object to be measured, measures a near electromagnetic field distribution of the object to be measured, and outputs a measurement result as an electromagnetic field distribution image (for example, see Japanese Patent Laid-Open No. 2000-74969). The device can be used to identify a large area of a near electromagnetic field of the object to be measured based on the electromagnetic field distribution image, and evaluate the electromagnetic field emitted from the object to be measured. Also, a method for estimating a far field measurement standard value from a near electromagnetic field of an object to be measured includes a method for calculating an electric current value of an electromagnetic wave generating source based on a near electromagnetic field of an object to be measured, and estimating a far field measurement standard value (for example, see Japanese Patent Laid-Open No. 2002-277550).
However, when the electromagnetic wave generating source is not an electric current source but a magnetic current source, this method cannot estimate a far field measurement standard value with high accuracy. Also, this method takes measures for current distribution, and it cannot be determined whether an area against which the measures are taken radiates noise as an electric current source or as a magnetic current source. Thus, unfortunately, the electromagnetic wave generating source cannot be correctly determined, and effective measures cannot be taken against EMI radiation.